Dual-component magnetic brush developing device
A dual-component magnetic brush developing device using a dual-component developer containing magnetic carriers and toner electrically attracted to the magnetic carriers. The dual-component magnetic brush developing device comprises: a magnetic field generation member being formed with a plurality of magnetic poles almost equally spaced from each other on a peripheral surface; a developer transport member being supported outside the magnetic field generation member for circumferential rotation and moving together with the magnetic field generation member at least in a developing area facing the image carrier in the proximity thereof; toner supply means for supplying an excess of new toner to magnetic carriers supported on the developer transport member and passing through the developing area; magnetic field reduction unit for reducing a magnetic field strength in the vicinity of a surface of the developer transport member by an agitation section for agitating the developer to which the excessive toner is supplied; and excessive toner separation unit being disposed downstream from the agitation section in a circumferential rotation direction of the developer transport member for separating excessive toner from the magnetic carriers supported on the developer transport member.
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Claims
1. A dual-component magnetic brush developing device using a dual-component developer containing magnetic carriers and toner electrically attracted to the magnetic carriers for selectively transferring the toner to an electrostatic latent image formed on an image carrier for visualizing the latent image, said dual-component magnetic brush developing device comprising:
- a magnetic field generation member being formed with a plurality of magnetic poles almost equally spaced from each other on a peripheral surface and being supported so that the peripheral surface makes a circumferential rotation move;
- a developer transport member being supported outside said magnetic field generation member for circumferential rotation and moving together with said magnetic field generation member at least in a developing area facing the image carrier in the proximity thereof;
- toner supply means for supplying an excess of new toner to the magnetic carriers supported on said developer transport member and passing through the developing area;
- magnetic field reduction means for reducing a magnetic field strength in the vicinity of a surface of said developer transport member by an agitation section for agitating the developer to which the excessive toner is supplied; and
- a plate-like member disposed downstream from the agitation section in a circumferential rotation direction of said developer transport member and placed in contact with or in the proximity of said developer transport member along said developer transport member where the developer is magnetically attracted to said magnetic field generation member through said plate-like member and charge-failure toner is liberated from the developer as the developer is agitated by a magnetic force on said plate-like member, forming a stable magnetic brush on said developer transport member,
- wherein said stable magnetic brush is transported to a developing area for transfer to an electrostatic latent image as said developer transport member makes a circumferential rotation.
2. The dual-component magnetic brush developing device as claimed in claim 1, wherein said magnetic field reduction means is a guide member for guiding said developer transport member so that said developer transport member moves away from a surface of said magnetic field generation member.
3. The dual-component magnetic brush developing device as claimed in claim 1, wherein said magnetic field reduction means is a magnetic member being placed between said magnetic field generation member and said developer transport member.
4. The dual-component magnetic brush developing device as claimed in claim 1 wherein said magnetic field generation member comprises an alternating pattern of magnetized S and N poles almost equally spaced 3 mm or less apart in a circumferential direction.
5. The dual-component magnetic brush developing device as claimed in claim 1 further including means for shaking said plate-like member.
6. The dual-component magnetic brush developing device as claimed in claim 1 further including toner recovery and transport member for recovering toner separated by said excessive toner separation means and transporting the toner to the agitation section.
7. The dual-component magnetic brush developing device as claimed in claim 1, wherein said excessive toner separation means is placed at a position where toner separated from the developer moves to the agitation section by gravitation.
8. The dual-component magnetic brush developing device as claimed in claim 1, wherein the toner excessively supplied to the developer passing through the developing area is supplied so that coverage percentage of toner to carriers is set in the range of 100% to 500%.
9. The dual-component magnetic brush developing device as claimed in claim 1, wherein said magnetic field generation member is a magnetic roller and wherein said developer transport member is an endless belt.
10. The dual-component magnetic brush developing device as claimed in claim 1, wherein said magnetic field generation member and said developer transport member are each an endless belt supported for circumferential rotation.
11. A dual-component magnetic brush developing device using a dual-component developer containing magnetic carriers and toner electrically attracted to the magnetic carriers for selectively transferring the toner to an electrostatic latent image formed on an image carrier for visualizing the latent image, said dual-component magnetic brush developing device comprising:
- a magnetic field generation member being formed with a plurality of magnetic poles almost equally spaced from each other on a peripheral surface and being supported so that the peripheral surface makes a circumferential rotation move;
- a developer transport member being supported outside said magnetic field generation member for circumferential rotation and moving together with said magnetic field generation member at least in a developing area facing the image carrier in the proximity thereof;
- magnetic field reduction means for reducing a magnetic field near a surface of said developer transport member after the developer is supported on said developer transport member and passes through the developing area, and stripping off the developer from said developer transport member; and
- toner supply means for supplying a predetermined amount of toner to maintain toner concentration in the developer having a magnetic developer agitation member disposed downstream from said magnetic field reduction means in the move direction of said developer transport member,
- said magnetic developer agitation member having a magnetic roll fixedly supported and a cylindrical sleeve rotatably supported outside said magnetic roll, said magnetic developer agitation member attracts the developer on said sleeve by a magnetic field of said magnetic roll and the developer attracted on said sleeve is transported by rotation of said sleeve forming a magnetic brush of the developer that is supplied to said developer transport member and a developing area.
12. The dual-component magnetic brush developing device as claimed in claim 11 wherein said magnetic field generation member comprises an alternating pattern of magnetized S and N poles almost equally spaced 3 mm or less apart in a circumferential direction.
13. The dual-component magnetic brush developing device as claimed in claim 11, further including a paddled developer agitation member disposed downstream from said magnetic field reduction means in the move direction of said developer transport member, said paddled developer agitation member having a paddle rotatably supported in an axial direction and rotated, agitating the developer replenished with toner from a toner hopper toward said magnetic developer agitation member.
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Type: Grant
Filed: Nov 25, 1996
Date of Patent: May 12, 1998
Assignee: Fuji Xerox Co., Ltd. (Tokyo)
Inventors: Takeshi Sumikawa (Ashigarakami-gun), Isao Ito (Ashigarakami-gun)
Primary Examiner: Nestor R. Ramirez
Law Firm: Oliff & Berridge, P.L.C.
Application Number: 8/754,935
International Classification: G03G 1509; G03G 15095;